Electronic devices often contain wireless communications capabilities. For example, portable electronic devices are often provided with wireless local area network (WLAN) communications circuitry, cellular telephone communications circuitry, and satellite navigation system receiver circuitry such as Global Positioning System (GPS) receiver circuitry. Using wireless communications circuits such as these, a user may communicate with local and remote wireless networks and may receive signals from GPS satellites.
As an example, a cellular telephone may include cellular telephone transceiver circuitry that is used to make telephone calls. The cellular telephone transceiver circuitry includes power amplifier circuitry that is used to amplify radio-frequency (RF) signals so that the RF signals can be transmitted to a nearby base station. If care is not taken, a change in temperature resulting from operation of the power amplifier circuitry can adversely affect the cellular telephone's ability to transmit RF signals at desired output power levels.
Consider a scenario in which a cellular telephone transmits RF signals to a current serving base station when the cellular telephone has an internal temperature of 40° C. The transmitted signals may be received by the current serving base station at a satisfactory power level of −10 dBm. As the power amplifier circuitry transmits the RF signals to the base station and generates heat in the process, the internal temperature of the cellular telephone may increase over time. When the internal temperature of the cellular telephone reaches 55° C., the radio-frequency signals that are transmitted by the cellular telephone may be received by the current serving base station at an unacceptably low power level of −15 dBm. As shown in this example, a change in the internal temperature of the cellular telephone can degrade the wireless output capability of the cellular telephone.
It would therefore be desirable to be able to provide ways for operating a wireless electronic device while taking into account variations in the operating temperature.